The field of the invention relates to electric brake controls for towed vehicles wherein the rate of vehicle deceleration is automatically sensed to produce a pulsed electric brake actuation of the brakes of the towed vehicle.
The braking of towed vehicles, such as trailers, is produced by several types of systems. In commercial truck vehicles, such as semitrailers, the trailer brakes are normally pneumatically or vacuum operated, and are directly connected to the braking system of the towing tractor. With smaller towed trailers, particularly those of the type towed by automobiles, such as utility trailers, boat trailers, and recreational vehicle trailers, it is well known to employ electric brakes on the trailer wheels to improve the stopping characteristics. Such automobile-trailer braking systems usually employ electric solenoid operated brakes with the trailer, and an electric brake controller mounted in the automobile adjacent the steering column is usually connected to the automobile hydraulic braking system for automatic operation by the automobile braking system, and also usually includes a manual control whereby the trailer brakes may be actuated separately from the automobile brakes.
Electric trailer brake controllers operated by automobile hydraulic brake systems are relatively complicated to install in that connection to the automobile braking system is required. Additionally, as the braking characteristics of an automobile hydraulic system vary as the automobile brake shoes wear, known available towed vehicle braking systems of the aforementioned type have not proven completely reliable in operation and leave much to be desired with respect to sensitivity of operation, optimum braking application, and safety. This type of system is difficult to adjust so that the proper amount of trailer braking is produced under all conditions of automobile braking, and under adverse road conditions where the road surface is wet or slippery braking situations may arise where known trailer brake systems actually produce unsafe braking characteristics and may cause the trailer to "jacknife".
Various towed vehicle braking systems have been proposed wherein the braking of the trailer is automatically controlled by the sensing of deceleration forces. U.S. Pat. Nos. 2,242,153; 2,642,961; 2,779,443; 2,856,036 and 2,969,857 disclose automatic brake applying apparatus wherein the deceleration inertial force imposed upon the hitch by the trailer during deceleration of the towing vehicle is sensed and used to produce a braking of the towed vehicle. Such systems as disclosed in these patents have not enjoyed commercial success, and their complexity and limitations of operation have rendered the same generally unacceptable from a practical point of view.
It has also been proposed to use pendulum or mass movement sensing devices for sensing deceleration of a towed and towing vehicle wherein the pendulum operates a braking circuit of the towed vehicle, either mechanical or electric, in dependence upon the degree of the deceleration occurring. U.S. Pat. Nos. 2,870,876 and 3,053,348 disclose such pendulum sensing systems. While such pendulum type systems have the capability of a higher degree of sensitivity than inertia force towed vehicle braking systems associated with the trailer hitch, the systems of such known pendulum type patents also include limitations in operating and manufacturing characteristics rendering the same commercially impractical.